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From: @S1-A.ARPA:host.MIT-MC.ARPA
Newsgroups: net.space
Subject: Gravity Slingshots
Message-ID: <1742@mordor.UUCP>
Date: Fri, 10-May-85 13:11:29 EDT
Article-I.D.: mordor.1742
Posted: Fri May 10 13:11:29 1985
Date-Received: Sun, 12-May-85 02:28:30 EDT
Sender: daemon@mordor.UUCP
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From: king@Kestrel.ARPA

In what follows I will assume that the traveler wants to enlarge
his/her/its orbit (No Carbon Chauvanism!)

Heuristically, you gain in two ways from a gravity slingshot:

1> Suppose you don't ignite your rocket, but you pass the massive
object on its trailing side in its orbit.  You get a forward component
to your velocity vector.  In the object's frame of reference, your
speed remains the same but your direction has shifted "forward".

2> If you accelerate at perigee, you add to your speed.  You could have
done that burning anywhere, but in addition to the additional speed YOU
LOSE LESS SPEED CLIMBING OUT OF THE GRAVITY WELL THAN YOU GAINED GOING
IN, BECAUSE YOU CLIMB OUT FASTER THAN YOU WENT IN.

-dick